a) Field of the Invention
The invention is directed to a closure device for vacuum closure of at least one opening in a wall, comprising a valve plate which is associated with a respective opening and which is displaceable between an open position in which it releases the opening, a position in which it covers the opening but is raised from the wall, and a closed position in which it covers the opening and contacts the wall, at least one piston-cylinder unit which serves to displace the valve plate between its open position and its position in which it covers the opening but is raised from the wall and which comprises a pneumatically actuated piston which is arranged in a cylinder housing and which is outfitted with a piston rod leading out of the cylinder housing through a bore hole, at least one carrier unit which is connected to the piston rod of the at least one piston-cylinder unit and which is associated with a respective valve plate, has at least one cylinder bore hole in which is arranged a pneumatically actuated piston which serves to displace the valve plate between its position in which it covers the opening but is raised from the wall and its closed position and which is outfitted with a piston rod leading out of the carrier unit through a bore hole, the valve plate being fastened to this piston rod.
b) Description of the Related Art
A closure device of the type mentioned above is known from U.S. Pat. No. 6,056,266 A. This closure device serves particularly as a door on the outside of a vacuum installation. The sequence of movements of the two piston-cylinder units which produce the L-shaped movement of the valve plate is controlled by means of a sequence control in such a way that the movements of the two piston-cylinder units proceed successively in the correct sequence.
Further, DE 196 33 798 A1 discloses a closure device for vacuum closure of an opening in a wall in which a housing is supported so as to be swivelable relative to the wall. First cylinder bore holes in which pneumatic pistons are supported so as to be displaceable are formed in the housing, and the piston rods of the pneumatic pistons carry the valve plate. The valve plate is displaced by means of these pistons between an open position in which the opening is released and a position in which the valve plate covers the opening but is raised from the wall. Second cylinder bore holes in which pneumatic pistons serving to swivel the housing are supported so as to be displaceable are provided in the housing. By actuating these pneumatic pistons, the housing can be swiveled so that the valve plate is pressed against the wall and the opening is closed in a vacuum-tight manner. A closure device of this kind can likewise be used as a door of a vacuum chamber. DE 196 33 798 A1 also describes an application as a valve arranged inside the vacuum.
When closure devices such as these which are described in U.S. Pat. No. 6,056,266 A and DE 196 33 798 A1 are to be used in applications in which there can be a vacuum on both sides of the opening in the wall, there is a considerable risk of leakage in the piston-cylinder units which are accordingly located in the vacuum area. The risk of leakage is present especially because of the increased pressure of the compressed air acting upon the piston. The resulting difference in pressure relative to the vacuum is substantially greater than the atmospheric pressure so that the risk of leakage is substantially higher. The damage which could occur in case of leakage is also generally greater compared to a leak relative to the atmosphere, since the pressure in case of a leak in the vacuum chamber is considerably greater than the atmospheric pressure so that, for example, bending of the chamber walls or additional leaks, e.g., in the area of welds, can occur.
Another closure device for vacuum closure of at least one opening in a wall is known from U.S. Pat. No. 6,427,973 B1. This closure device is also particularly suitable for closing and releasing a plurality of slot-shaped openings. A carrier plate which is displaceable in the plane of the wall, for example, by means of a tappet drive encapsulated in bellows, is provided for this purpose. Closure plates associated with the respective openings are supported at the carrier plate so as to be displaceable in the direction vertical to the wall, and the closure plates have guide pins which slide in corresponding bushings fastened to the carrier plate. A tight, expandable cylinder space is formed between the carrier plate and a respective closure plate by means of a bellows. The opening in the wall is closed in a vacuum-tight manner by admitting compressed air into this cylinder space. There can be a vacuum on both sides of the wall (in the closed state of the valve device as well as in the opened state of the valve device). This device is disadvantageous particularly in that the bellows forming the cylinder spaces must be constructed so as to be very stable in order to absorb the pressure of the compressed air admitted into the cylinder space. Also, there is a considerable risk of leakage in bellows of this kind particularly after an extended period of use and compressed air can escape into the vacuum chamber in case of leaks.
A further disadvantage in this valve device is that the closure plates can only be exchanged with difficulty. However, it is necessary to exchange the closure plate occasionally particularly when aggressive process gases are used. Also, the spaces encapsulated by the diaphragm bellows can only be accessed with difficulty.
Further, linear leadthroughs are known in which two sealing rings are arranged at a distance from one another between the part that is guided through and the wall of the vacuum chamber and the space between the two sealing rings is pumped out by means of a pump and a line leading into this space. This is intended to reduce the gas brought through the linear leadthrough into the vacuum.